Orchestrating a patch installation scenario in a application sever cluster

[Kapil Thangavelu]

The intra service unit coordination for a round robin activity is best
served by a peer relation. The signalling of the patch application/change
needs to be done externally via the client api atm, ie. changing the
service configuration to denote a vcs revision or patch file.

A subordinate isn't needed. Subordinates are helpful for generic or
ancillary features, but structuring core functionality of another service
there tends to obfuscate the charm and the usage imo.

cheers,
Kapil


On Tue, May 21, 2013 at 9:26 AM, Denis Weerasiri <ddweerasiri at gmail.com>wrote:

> Hi,
> I am trying to realize the following patch installation scenario in a
> application cluster fronted with a load-balancer.
> Let's assume I use Puppet like a configuration management tool to install
> the patch in each node.
>
> Here is the scenario
>
>    - The cluster is consist of two nodes named A and B.
>    - First stop the node A and install the patch using a puppet manifest
>    and restart the node A
>    - Then stop the node B and install the patch using a puppet manifest
>    and restart the node B
>    - So the application is available 100% at all the times
>
> The problem is, how can I write a charm to automate this patch
> installation scenario, where *Juju should be able to
> propagate life-cycle changes in one service unit in Node A to the other
> service unit in Node B*.
> When I went through the Juju doc, I found about subordinate services which
> may solve my problem
> https://juju.ubuntu.com/docs/subordinate-services.html . Is this the
> correct way of automating this patch installation scenario?
> Or how is it possible to propagate life-cycle changes in one service unit
> to the another service unit?
>
>
>
> --
> Thanks,
> Denis
> ----------------------------------------------------------
> *Denis Weerasiri*
> *
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